Also a vote for A/B testing to keep up with other email providers. To start I would think random list split testing to do subject line testing for opens, and text/image link testing for clicks would be most desirable. Nothing fancy, just what does better.

I would like to have A/B testing for email subject and for date/time of sending

An absolute "MUST HAVE". This can be used for incrementally and iteratively improving messaging. Upvoted.

I also think this would work extremely well with a Campaign Tab feature I have requested. If anyone reading this would take a look at that, I've even done a rendering of how it could look, and I would appreciate any additional thoughts you could contribute and enhance the request with.

A/B Testing would be great - ideally we should be able to test any modification (images, headlines, buttons, order of content) and most critically, be able to compare Open rate, CTR, Unsubscribes, Link clicks, and conversion rate.

Currently I split 1% of my mailing list out into 4 segments, but it is bad for list integrity. If for example we could exclude lists from emails this would help, so I can leave them in the main list, and exclude them from the final mailout if they are in one of the segments. That's just a little awkward and error prone.

Why is this still "under review" after years? You know you are going to have to add this functionality to stay competitive.

You can even use the crawl-walk-run approach and just do something basic to start that at least gets us subject line?

A/B testing at least for subject line. 5% for A, 5% for B and after 5m gatbering results the rest (90%) with the BEST subject line

This would be great for subject lines and content to test open rate and conversion.